Zoom lens and image pickup apparatus including the zoom lens

Abstract

A zoom lens includes, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a rear lens group including one or more lens units. During zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that an interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end. The third lens unit includes a positive lens and a negative lens. Image forming magnifications β2W and β2T of the second lens unit at the wide-angle end and at the telephoto end, image forming magnifications β3W and β3T of the third lens unit at the wide-angle end and at the telephoto end, a focal length f2 of the second lens unit, and a focal length fT of the entire zoom lens at the telephoto end are appropriately set.

What is claimed is: 
     
       1. A zoom lens comprising, in order from an object side to an image side:
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; and 
 a rear lens group including one or more lens units, 
 wherein during zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that an interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, 
 wherein the third lens unit includes a positive lens and a negative lens, and 
 wherein, when β2W and β2T are image forming magnifications of the second lens unit at the wide-angle end and at the telephoto end, respectively, β3W and β3T are image forming magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, f2 is a focal length of the second lens unit, fT is a focal length of the entire zoom lens at the telephoto end, f3 is a focal length of the third lens unit and fW is a focal length of the entire zoom lens at the wide-angle end, the following conditions are satisfied:
   0.10<(β2 T/ β2 W )/(β3 T/ β3 W )<1.65
 
   0.01 <|f 2| /fT< 0.15, 
   0.5 <f 3/√( fW×fT )≦0.809.
 
 
 
     
     
       2. The zoom lens according to  claim 1 , wherein the following condition is satisfied:
   2.7<β3 T/β 3 W< 5.0.
 
 
     
     
       3. The zoom lens according to  claim 1 , wherein, when nd 3   i  and νd 3   i  are a refractive index and an Abbe number of a material of at least one positive lens included in the third lens unit, the following conditions are satisfied:
   1.54 <nd 3 i< 2.0 
   55 <νd 3 i< 100. 
 
     
     
       4. The zoom lens according to  claim 1 , wherein, when m 3  is an amount of movement of the third lens unit during zooming from the wide-angle end to the telephoto end, the following condition is satisfied:
   0.5 <|m 3|/√( fW×fT )<2.0.
 
 
     
     
       5. The zoom lens according to  claim 1 , wherein, when f3n is a focal length of at least one negative lens included in the third lens unit and f3 is a focal length of the third lens unit, the following condition is satisfied:
   0.1 <|f 3 n|/f 3<3.0. 
 
     
     
       6. The zoom lens according to  claim 1 , further comprising an aperture stop configured to move integrally with the third lens unit during zooming, which is located on the object side of the third lens unit,
 wherein, when TDT is a total length of the zoom lens at the telephoto end and DSP is an air-equivalent distance from the aperture stop to an image plane at the telephoto end, the following condition is satisfied:
   0.3 <DSP/TDT< 0.8. 
 
 
     
     
       7. The zoom lens according to  claim 1 , wherein, when f1 is a focal length of the first lens unit, the following condition is satisfied:
   0.2 <f 1 /fT< 1.2. 
 
     
     
       8. The zoom lens according to  claim 1 , wherein the rear lens group consists of a fourth lens unit having a positive refractive power, and
 wherein the fourth lens unit moves during zooming. 
 
     
     
       9. The zoom lens according to  claim 1 , wherein the rear lens group consists of a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power, and
 wherein the fourth lens unit and the fifth lens unit move during zooming. 
 
     
     
       10. An image pickup apparatus comprising:
 a zoom lens; and 
 an image sensor located at an image plane of the zoom lens and configured to receive an image formed by the zoom lens, 
 wherein the zoom lens comprises, in order from an object side to an image side; 
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; and 
 a rear lens group including one or more lens unit, 
 wherein during zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that in interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, 
 wherein, the β2W and β2T are image forming magnifications of the second lens unit at the wide-angle end and at the telephoto end, respectively, β3W and β3T are image forming magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, f2 id a focal length of the second lens unit, fT is a focal length of the entire zoom lens at the telephoto end, f3 is a focal length of the third lens unit and fW is a focal length of the entire zoom lens at the wide-angle end, the following conditions are satisfied:
   0.10 <(β2T/β2W)/(β3T/β3W) <1.65
 
   0.01 <lf2l/fT <0.15, 
   0.5 <f3/√(fW ×fT)<0.809.
 
 
 
     
     
       11. A zoom lens comprising, in order from an object side to an image side:
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; and 
 a rear lens group including one or more lens units, 
 wherein during zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that an interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, 
 wherein the third lens unit includes a positive lens and a negative lens, and 
 wherein, when β2W and β2T are image forming magnifications of the second lens unit at the wide-angle end and at the telephoto end, respectively, β3W and β3T are image forming magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, f2 is a focal length of the second lens unit, fT is a focal length of the entire zoom lens at the telephoto end, and nd 3   i  and νd 3   i  are a refractive index and an Abbe number of a material of at least one positive lens included in the third lens unit, the following conditions are satisfied:
   0.10<(β2 T/ β2 W )/(β3 T/ β3 W )<1.65
 
   0.01 <|f 2 |/fT< 0.15 
   1.54 <nd 3 i< 2.0 
   55 <νd 3 i< 100. 
 
 
     
     
       12. An image pickup apparatus comprising:
 a zoom lens; and 
 an image sensor located at an image plane of the zoom lens and configured to receive an image formed by the zoom lens, 
 wherein the zoom lens comprises, in order from an object side to an image side; 
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; and 
 a rear lens group including one or more lens unit, 
 wherein during zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that in interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, 
 wherein the third lens unit includes a positive lens and a negative lens, and 
 wherein, when β2W and β2T are image forming magnifications of the second lens unit at the wide-angle end and at the telephoto end, respectively, β3W and β3T are image forming magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, f2 is a focal length of the second lens unit, fT is a focal length of the entire zoom lens at the telephoto end, and nd 3   i  and νd 3   i  are a refractive index and an Abbe number of a material of at least one positive lens included in the third lens unit, the following conditions are satisfied:
   0.10<(β2T/β2W)/(β3T/β 3 W)<1.65
 
   0.01<lf2l/fT<0.15 
   1.54<nd3i<2.0 
   55<vd3i<100. 
 
 
     
     
       13. A zoom lens comprising, in order from an object side to an image side:
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; 
 a fourth lens unit having a negative refractive power; and 
 a fifth lens unit having a positive refractive power, 
 wherein during zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that an interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, and the fourth lens unit and the fifth lens unit move, 
 wherein the third lens unit includes a positive lens and a negative lens, and 
 wherein, when β2W and β2T are image forming magnifications of the second lens unit at the wide-angle end and at the telephoto end, respectively, β3W and β3T are image forming magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, f2 is a focal length of the second lens unit, and fT is a focal length of the entire zoom lens at the telephoto end, the following conditions are satisfied:
   0.10<(β2T/β2W)/(β3T/β3W)<1.65
 
   0.01<|f2|/fT<0.15. 
 
 
     
     
       14. An image pickup apparatus comprising:
 a zoom lens; and 
 an image sensor located at an image plane of the zoom lens and configured to receive an image formed by the zoom lens, 
 wherein the zoom lens comprises, in order from an object side to an image side: 
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; 
 a fourth lens unit having a negative refractive power; and 
 a fifth lens unit having a positive refractive power, 
 wherein during zooming, the first lens unit moves along a locus convex towards the image side, and the second lens unit and the third lens unit move such that an interval between the first lens unit and the second lens unit becomes larger at a telephoto end than at a wide-angle end and an interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, and the fourth lens unit and the fifth lens unit move, 
 wherein the third lens unit includes a positive lens and a negative lens, and 
 wherein, when β2W and β2T are image forming magnifications of the second lens unit at the wide-angle end and at the telephoto end, respectively, β3W and β3T are image forming magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, f2 is a focal length of the second lens unit, and fT is a focal length of the entire zoom lens at the telephoto end, the following conditions are satisfied:
   0.10<(β2T/β2W)/(β3T/β3W)<1.65
 
   0.01<|f2|/fT<0.15.